This invention relates to joints used with composite structural members which are commonly used to form strong, yet lightweight structures.
Composite structural members comprise a number of fibers made of a high tensile and compressive strength material such as glass or carbon, encased within a suitable resin matrix. Often a number of resin and fiber layers are used to provide the desired strength. Other composite structural materials include a core material sandwiched between sheets which may or may not be composites themselves. A patent that shows a composite structural member is Hulls, U.S. Pat. No. 5,041,318, "Composite Structural Member with Integral Load Bearing Joint-Forming Structure."
FIG. 1 is a cross-sectional view of a prior art structure using pultruded composite materials connected by a joint 2. The joint 2 is typically formed out of aluminum. The joint 2 connects flat preformed panels 4 and 6. In this example, the preformed panels comprise an outer skin portion 4a and 6a, an inner skin portion 4b and 6b and core materials 4c and 6c. The preformed panels 4 and 6 are attached to the joint 2 by adhesive layers 8 and 10, respectively. A problem with this type of joint 2 is that it may not adequately protect against the torsion loads caused by uneven roads and bumps encountered by a tractor trailer truck or the bending forces caused by loads in the trailer. In this conventional joint, these loads show up as bending loads at the joint 2. These bending loads cause pressure at the skins of the preformed panels 4 and 6 at points 12 and 14. These bending loads may urge the panel skins together crushing the core or urge the skins apart causing them to separate from the core material.
A common example of a structure made up of a series of joint panels is a semi-trailer, illustrated diagrammatically in FIG. 2. The load on the floor of the trailer 20 will cause the floor to deflect downward. The resulting forces being tension at the edge pieces of the floor and compression on the upper edge. For this reason, in the conventional trailer construction as shown in FIG. 1, the corner joints are made sufficiently stiff so that they carry virtually all the compressive and tension load. The size and resulting stiffness of the of the corner joint is such that the wall panels make little contribution to the load carrying structure. The wall panels, however, do function in shear between the compressive and tensile members as shown in FIG. 2.